Dating of photograph
By 1871, the gelatin dry plate method made exposure times short enough that cameras could be hand held (ie, fraction of a second).
By 1878, technology shortened exposure times to a fraction of a second, about 1/25th of a second.
Photographs are researched by working with the format or type of mount, the type of photograph, the props in the photograph, the fashions people are wearing and the hairstyles of the men and women.
Military and occupational photographs reveal the persons occupation or the regiment of a soldier, along with a timeframe when they served or worked.But it's also reasonable to assume it wasn't too long after 1878 before most photographers were using equipment that allowed them to photograph with exposures of at least only a few seconds, or even a fraction of a second.So why aren't there more photographs of people smiling or moving around from the late 19th century?Have you ever seen "The Horse in Motion", a sequence of photographs of a horse and rider at a gallop, analyzing it's gait frame by frame (shown above)? Without getting too technical, anything that is fast enough to capture and freeze the motion of a galloping horse is more than fast enough to capture a smile or movement of a human being.Of course, it's reasonable to assume that not all photographers had the most advanced equipment the moment it became available.